Waterborne dispersions are utilized in the coatings industry to provide substrates with aesthetic beauty, solvent and chemical resistance, mar and scuff resistance, and abrasion resistance. Such waterborne dispersions are commonly used for coating wood, masonry, plastic, textile, and metal products and can also be used in ink jet ink compositions. In recent years, waterborne dispersions have come into favor from an environmental standpoint as replacements for oil based coating compositions because they can be formulated with a low level of volatile organic compounds (VOCs) and are preferably free of volatile organic compounds.
The current trends in performance coatings are directed to environmentally friendly polymer types that contain a high content of raw materials based on renewable resources which can form coalesced films with low or reduced emissions of volatile organic compounds. Coatings of this type, accordingly, have reduced environmental impact. However, today waterborne polymers that offer reduced emissions of volatile organic compounds during film formation are typically based on petroleum derived raw materials or lack the performance needed in certain applications, such as wood flooring. This is particularly true in the case of one component self-crosslinking compositions which are more user friendly due to reduced toxicity concerns and more environmentally friendly due to less waste generated as compared to more conventional two component systems.
U.S. Pat. Nos. 4,066,591 and 4,147,679 disclose the preparation of waterborne polyurethane dispersions which contain unsaturated functional groups capable of undergoing auto-oxidative crosslinking.
U.S. Pat. No. 4,598,121 discloses a method for preparing an aqueous polyurethane dispersion, comprising (a) preparing a prepolymer with free NCO groups by reacting an aliphatic or cycloaliphatic polyisocyanate with a polyol, and an anionic compound; (b) dispersing said prepolymer in water; (c) reacting said water-dispersed prepolymer with a diamino hydrazide as a chain lengthening agent; and (d) reacting the prepolymer of step (e) in said dispersion with formaldehyde to effect crosslinking.
U.S. Pat. No. 4,983,662 discloses an aqueous self crosslinkable coating composition comprising an aqueous dispersion of at least one polyurethane and having hydrazine (or hydrazone) functional groups and carbonyl functional groups, disposed therein, to provide a self crosslinking reaction in which the polyurethane polymer takes part via azomethine formation during and/or after film formation.
U.S. Pat. No. 5,141,983 discloses a ketone-hydrazide crosslinking technology where the ketone, or carbonyl group resides on an acrylic polymer and a polyurethane polymer contains hydrazide functional groups. The composition is obtained by polymerizing the acrylic monomers in the presence of an aqueous polyurethane dispersion.
U.S. Pat. Nos. 5,571,861 and 5,623,016 disclose an aqueous, self-crosslinking polymer dispersion binder(s) comprising polyhydrazides and carbonyl-containing polyurethane-vinyl hybrid polymers and also, if desired, conventional additives are useful in base coatings, aqueous coatings, adhesives and printing inks.
U.S. Pat. No. 6,239,209 discloses waterborne urethane-acrylic compositions which are auto-oxidatively crosslinkable. In one embodiment, the composition also contains ketone hydrazide type self-crosslinking where the ketone/carbonyl is introduced via the acrylic and the hydrazide functionality is contained on the polyurethane along with the unsaturated oxidatively curable functional groups.
U.S. Pat. No. 6,576,702 discloses waterborne polyurethane dispersions are prepared by reacting (1) at least one polyisocyanate; (2) at least one active hydrogen containing compound, such as a polyol or a polyamide; and (3) preferably also at least one water-dispersibility enhancing compound having water-dispersion enhancing groups, in order to form an isocyanate terminated prepolymer. The prepolymer subsequently is (1) optionally neutralized by reaction with at least one neutralizing agent, (2) dispersed in water, and then (3) chain extended by reaction with at least one of water, inorganic or organic polyamine having an average of about 2 or more primary and/or secondary amine groups, or combinations thereof. At least one plasticizer is introduced into the reaction mixture at any time during prepolymer formation or before the prepolymer is dispersed in water. The plasticizer substantially or completely replaces other organic diluents or solvents. Various types of plasticizers may be employed, including reactive plasticizers.
United States Patent Application Publication No. 2010/0330375 discloses aqueous polyurethane dispersions that are made from urethane prepolymers comprising one or more polyhydroxy compounds from ketone functional molecules derived from an epoxidized natural oil. Addition of a hydrazine functional moiety to the prepolymer dispersion can further provide a crosslinking mechanism resulting in the formation of azomethine linkages in the resulting polyurethane during drying. When the ketone functional molecule is derived from levulinic acid and epoxidized vegetable oil, the resulting urethane dispersion can also be converted into a hybrid polyurethane-vinyl dispersion by adding and polymerizing one or more vinyl monomers in the polyurethane prepolymer or polyurethane dispersion. United States Patent Application Publication No. 2010/0330375, more specifically, reveals an aqueous polyurethane dispersion comprising at least one polyol obtained from the reaction of an epoxidized natural oil with an organic acid, wherein the polyol is reacted with a polyisocyanates to form a portion of the polyurethane. The novel aqueous polyurethane compositions and polyurethane-acrylic compositions, revealed by United States Patent Application Publication No. 2010/0330375, can provide a clean high quality dispersion (low in sediment) that quickly self-crosslinks at ambient or low temperatures. Additionally, they are storage stable, have good color stability, and can be formulated with a low volatile organic component content and use significant amounts of renewable raw materials as building blocks.
The main building block of the waterborne polyurethane and urethane-acrylic dispersions, disclosed by United States Patent Application Publication No. 2010/0330375, is a poly-ketone polyol obtained from the reaction of levulinic acid with epoxidized or epoxy functional natural oils, such as epoxidized soybean oil or epoxidized linseed oil. These oils offer the advantage of being renewable agricultural products. United States Patent Application Publication No. 2010/0330375 further indicates that veronica oil, which is a naturally occurring oil that contains epoxy functional groups, can be used as an alternative. It is well documented that levulinic acid is a significant renewable raw material which can be obtained from biomass in the so called “Biofine Process”. Both epoxidized soybean oil and epoxidized linseed oil are commercially available and are widely used as plasticizers for polyvinyl chloride. They, additionally, can act as a scavenger for hydrochloric acid which is liberated when polyvinyl chloride is heat treated. In any case, the polyurethane-acrylate compositions described by United States Patent Application Publication No. 2010/0330375 offer an excellent combination of characteristics and are made using a significant amount of renewable raw materials as building blocks. However, these polyurethane-acrylate compositions are relatively expensive and a lower cost alternative is needed which offers similar performance characteristics and which is derived to a significant extent from renewable resources.